The present work focuses on the therapeutic efficacy and the toxicity of alpha interferon in patients younger than age 18 years. 5 patients younger than 18 years were treated and followed up between 1990 and 1999 at the department of haematology (Aziza Othmana Hospital) Hydroxyurea was given as initial treatment to all patients. After a median period of 8 months, these patients received alpha interferon (5 millions units/m2 once). Six months after the beginning of the alpha interferon a complete hematologic response was obtained in all patients. The median overall survival was of 66 months: 3 patients are still alive (2 patients in an advanced stage and one patient in chronic phase) and 2 patients died after transformation. The most common reported side effects of alpha interferon were asthenia, weight loss, fever, myalgia, chills and headaches--these toxic manifestations were mild and were noticed in all our patients. Myelosuppression was noted in two patients. Interferon is well tolerated in patients younger than age years 18 old, with CML. It may offer an alternative to bone marrow transplantation in children in the chronic phase of CML without histocompatible donor. The role of new agents such as STI 571 needs to be evaluated as well.